Even as IS blew up the ancient city of Nimrud, south of Mosul, and published a video of the destruction on the internet, experts were warning that the looting and trade in antiquities out of IS-held areas of Iraq and Syria was more prominent now than ever before.

"They are very practical about what they destroy. They destroy things that are not easily marketable, and sell the portable antiquities," said Boston University professor Michael Danti, who is academic director at ASOR Cultural Heritage Initiatives, a programme set up by the US State Department.